Method For Spectroscopy Of Surface Plasmons In Surface Plasmon Resonance Sensors And An Element For The Use Of Thereof

ABSTRACT

A method and system for spectroscopy of surface plasmons is presented. An electromagnetic wave is made incident on a diffraction grating. Surface plasmons are excited on a medium coincident to the diffraction grating and dispersion of a wavelength spectrum of the electromagnetic wave are simultaneously performed through diffraction. Changes in spatial distribution of intensity in the wavelength spectrum of the diffracted electromagnetic wave due to the excitation of the surface plasmons are measured.

TECHNICAL FIELD

The invention relates to a method for spectroscopy of surface plasmons in surface plasmon resonance sensors and an element for the use of thereof.

BACKGROUND ART

Sensors belong to modern devices for measuring physical, chemical and biological quantities. Modern sensors such as electrical, optical and mechanical sensors rely on various methods. One of the approaches used in optical sensors is the spectroscopy of surface plasmons. Surface plasmons are electromagnetic waves, which can be excited at an interface between a metal and a dielectric medium (Raether Surface plasmons on smooth and rough surfaces and on gratings, Springer-Verlag, Berlin, 1988). As the electromagnetic field of surface plasmons is highly localized at the surface of the metal, surface plasmons are extremely sensitive to changes in optical parameters occurring in the vicinity of the surface of the metal. In optical sensors, surface plasmons are usually optically excited with an electromagnetic wave in the visible or near infrared spectrum. The resonant condition for excitation of surface plasmons with an electromagnetic wave depends on refractive index of the dielectric in the proximity of the metal surface. Therefore, variations in the refractive index can be monitored from changes in the interaction between an electromagnetic wave and a surface plasmon. Surface plasmon resonance (SPR) sensors can be used as highly sensitive refractometers and can also be applied for the study of biomolecules and their interactions and for detection of chemical and biological compounds. In these applications, SPR sensors are combined with biorecognition elements which specifically interact with an analyte (e.g., antibody, enzymes, DNA). Interaction between the immobilized biorecognition element on the sensor surface and an analyte in a liquid sample increases a refractive index in the proximity of surface of the sensor. This refractive index change can be detected by means of optically excited surface plasmons.

There are numerous configurations of surface plasmon resonance (SPR) sensors. These include configurations employing prism couplers (Sensors and Actuators, 4 (1983) 299-304; Electronics Letters, 23 (1988) 1469-1470), grating couplers (Sensors and Actuators B, 8 (1992) 155-160), optical fibers (Sensors and Actuators B, 12 (1993) 213-220; Analytical Chemistry, 66 (1994) 963-970) and integrated optical waveguides (Sensors and Actuators B, 12 (1993) 213-220; Analytical Chemistry, 66 (1994) 963-970). In grating-based SPR sensors, interaction between an electromagnetic wave and a surface plasmon is detected by measuring changes in intensity (Biosensors, 3 (1987/88) 211-225), angular spectrum (American Laboratory, 33 (2001) 37-40) or wavelength spectrum (Measurements and Science Technology, 6 (1995) 1193-1200) of an electromagnetic wave reflected from the grating coupler. For parallel detection of multiple chemical or biological compounds or for parallel monitoring of their interactions, multichannel SPR sensors are used. In multichannel SPR sensors using grating couplers, the resonant interaction between an electromagnetic wave and surfaces plasmons can be detected in spatial distribution of angular reflected spectrum (American Laboratory, 33 (2001) 37-40). Recently, a method for multichannel SPR sensor based on prism coupler and sequential excitation of surface plasmons was described in Czech patent No. 291 728 (J.

tyroký, J. Dostálek, J. Homola).

SUMMARY OF THE INVENTION

This invention concerns surface plasmon resonance sensors with the wavelength interrogation and grating coupler. The invention consists in an SPR sensor method for simultaneous excitation of surface plasmons with an electromagnetic wave and dispersion of spectrum of the electromagnetic wave. In this method, an electromagnetic wave is made incident on a diffraction grating where it is diffraction coupled to surface plasmons. Simultaneously, wavelength spectrum of the electromagnetic wave is spatially dispersed through diffraction on the grating. Changes in the spectrum of the electromagnetic wave induced by the excitation of surface plasmons are detected with the system measuring spectral distribution of the intensity of dispersed electromagnetic wave.

For this method, an electromagnetic wave is emitted from two or more monochromatic light-sources or from a source of polychromatic light. Electromagnetic wave is made incident on the surface of a sensor element with a diffraction grating where it excites surfaces plasmons within a narrow band of wavelengths. The excitation of surface plasmons is accompanied with a change in the intensity of diffracted electromagnetic wave within this wavelength band. Radiation of different wavelengths is diffracted away from the grating under different angles. Therefore, changes in the wavelength spectrum of the electromagnetic wave are converted to variations in the spatial distribution of intensity of the diffracted electromagnetic wave. These changes are detected with a system allowing the measurement of spatial distribution of electromagnetic radiation (such detection system is further referred to as a position-sensitive detector). The measurement of intensity distribution of diffracted electromagnetic radiation enables monitoring of evolution of the resonant interaction between the electromagnetic wave and surface plasmons and thus allows determining the sensor response.

The method is based on a sensor element which works both as a coupling and dispersing element. This sensor element encompasses a diffraction grating on which surface plasmons are excited with an electromagnetic wave incident on its surface and the wavelength spectrum of the electromagnetic wave is dispersed into different angles. This method is principally different from the existing SPR sensors with wavelength interrogation in which the sensor element serves only for excitation of surface plasmons and the spectral analysis of an electromagnetic wave is performed separately using a spectrograph with an independent dispersive element. The herein described method significantly simplifies the construction of SPR sensors.

The method for SPR sensor detection relies on a sensor element 1. This sensor element 1 enables excitation of surface plasmons 2 and angular dispersion of wavelength spectrum and can be realized as follows. An electromagnetic wave 3 in visible or near infrared spectrum propagates in a medium 4 and under an angle of incidence 10 it is incident at the sensor element 1 with a diffraction grating 6 and a metal layer 7. On the metal surface, there is a dielectric medium 5. On the relief diffraction grating 6, a narrow wavelength band of the electromagnetic wave 3 is diffraction-coupled to a surface plasmon 2 at the interface between a metal 7 and a dielectric medium 5. Simultaneously, the electromagnetic wave 3 is diffracted into a divergent beam 8. In the divergent beam 8, an electromagnetic radiation of different wavelengths propagates away from the grating under different angles. Within the diffracted beam 8, the intensity of electromagnetic radiation is changed within a narrow wavelength band due to the excitation of surface plasmons 2. Divergent beam 8 is made incident on a position-sensitive detector 9 which measures a spatial distribution of electromagnetic intensity. The excitation of surface plasmons 2 on the diffraction grating 6 is manifested as a change in the intensity distribution of diffracted electromagnetic beam 8 detected with the position-sensitive detector 9.

The method for SPR sensor using the above described sensor element 1 can be extended for multichannel sensor configuration by the following embodiments:

In the first embodiment, an electromagnetic wave 3 is made simultaneously incident on multiple sensing areas 12 with a diffraction grating 6. These sensor areas 12 are arranged parallel to the direction of propagation of surface plasmons 2. At different sensing areas 12, the electromagnetic wave 3 is diffracted to a series of spatially separated diverging electromagnetic beams 8 propagating away from the surface of the sensor element 1. These electromagnetic beams 8 are incident on different areas of the position-sensitive detector 9.

In the second embodiment, the electromagnetic wave 3 is made incident on multiple sensing areas 12 with a diffraction grating 6. These sensor areas 12 are arranged perpendicularly to the direction of propagation of surface plasmons. At different sensing areas 12, the electromagnetic wave 3 is diffracted to series of spatially separated diverging light beams 8 propagating away from the surface of sensor element 1. These light beams 8 are incident at different areas of the position-sensitive detector 9.

In the third embodiment, the electromagnetic wave is normally incident on multiple sensing areas 12 with diffraction gratings 6. In different sensing areas 12, different diffraction gratings 6 are oriented differently with respect to the center of a position-sensitive detector 9. At different sensing areas 12, the electromagnetic wave 3 is diffracted to a series of spatially separated diverging electromagnetic beams 8 propagating away from the surface of sensor element 1. Owing to the different orientation of diffraction gratings 6 in different sensing areas 12, diffracted diverging electromagnetic beams 8 are projected on different areas on the position-sensitive detector 9.

The sensor element 1 can be coated in at least one area by a layer 15 with molecules for detection or study of interaction of chemical or biological substances present in a sample 5 which is in the contact with the surface of sensor element 1.

Sensor element 1 for the method presented herein can be fabricated from glass by means of methods such as cutting, lapping, polishing, etching. Additionally, it can be fabricated from polymers by methods such as injection molding or hot embossing. Thin metal layers 7 supporting surface plasmons (e.g., gold, silver) and other optical layers can be prepared by methods such as vacuum evaporation or sputtering. As a position-sensitive detector 9, linear or two-dimensional detectors such as CCD, PDA or CMOS can be used. As a source of electromagnetic radiation light emitting diodes (LED), filament lamps or discharge lamps can be employed.

DESCRIPTION OF DRAWINGS

The invention is explained in the following drawings.

FIG. 1 depicts the method for SPR sensor detection using a sensor element 1 on which a relief diffraction grating 6 is prepared. On the diffraction grating 6, an incident electromagnetic wave 3 is coupled to surface plasmons 2 and is diffracted into a diverging beam 8. In the diffracted beam 8, electromagnetic radiation at different wavelengths is propagating from the surface of sensor element 1 at different directions. The excitation of surface plasmons and the dispersion of the electromagnetic wave 3 into the diverging beam 8 is realized through different diffraction orders of the grating.

FIG. 2 shows the method for multichannel SPR sensor detection using a sensor element 1 with multiple sensing areas 12 with a relief diffraction grating 6. At different sensing areas 12, the electromagnetic wave 3 is diffracted to a series of spatially separated diverging electromagnetic beams 8 propagating away from the surface of sensor element 1. These electromagnetic beams 8 are incident on different areas of a linear position-sensitive detector 13.

FIG. 3 shows the method for multichannel SPR sensor detection using a sensor element 1 with multiple sensing areas 12 with a diffraction grating 6. At different sensing areas 12, the electromagnetic wave 3 is diffracted to a series of spatially separated diverging electromagnetic beams 8 propagating away from the surface of sensor element 1. These electromagnetic beams 8 are incident on different areas of a two-dimesional position-sensitive detector 14.

FIG. 4 shows the method for multichannel SPR sensor detection using a sensor element 1 with multiple sensing areas 12 with a diffraction grating 6. In different sensing areas 12, the diffraction gratings 6 are oriented differently. At different sensing areas 12, the electromagnetic wave 3 is diffracted to a series of spatially separated diverging electromagnetic beams 8 propagating away from the surface of sensor element 1. Owing to different orientation of diffraction gratings 6 located in different sensing areas 12, diffracted diverging electromagnetic beams 8 are projected on different areas of a two-dimensional position-sensitive detector 14.

FIG. 5 shows the sensor element 1 as a planar slide 16 with an array of diffraction gratings 6.

EXAMPLES Example 1

FIG. 1 shows an embodiment of the method for SPR sensor detection using a sensor element 1 with a diffraction grating 6 which enables diffraction-coupling of an electromagnetic wave 3 to surface plasmons 2 and angular dispersion of the wavelength spectrum of the electromagnetic wave 3. Collimated electromagnetic wave 3 is made incident from an optical medium 4 at sensor element 1 under an angle 10. On the top of the sensor element 1, there is a periodic relief diffraction grating 6 coated with a metal layer 7. The grating 6 with a metal layer 7 is in the contact with a dielectric medium 5. At the interface between the metal 7 and the dielectric 5, the electromagnetic wave 3 excites surfaces plasmons 2 within a narrow band of wavelengths through the second diffraction order. The excitation of surface plasmons 2 is accompanied with absorption of energy of the electromagnetic wave 3 at these wavelengths. Simultaneously, upon the incidence on the relief diffraction grating 6, the electromagnetic wave 3 is diffracted into the first diffraction order which forms a diverging electromagnetic beam 8. In this electromagnetic beam 8, radiation of different wavelengths propagates away from the surface of sensor element 1 at different angles. In the dispersed wavelength spectrum an intensity change occurs at wavelengths at which the electromagnetic wave 3 is coupled to surface plasmons 2. The angular dispersed wavelength spectrum can be measured using a position-sensitive detector 9.

Example 2

FIG. 2 shows an embodiment of the method for multichannel SPR sensor detection using a sensor element 1 with multiple sensing areas 12 with a diffraction grating 6 which enables the coupling of electromagnetic wave 3 to surface plasmons 2 and angular dispersion of wavelength spectrum of the electromagnetic wave 3. Collimated electromagnetic wave 3 is made simultaneously incident on multiple sensing areas 12 which are arranged parallel to the direction of propagation of surface plasmons. Through diffraction on gratings 6, in different sensing areas 12 the electromagnetic wave 3 is coupled to spatially separated divergent electromagnetic beams 8. The diffracted beams 8 propagate away from the surface of the sensor element 1 and are incident on different areas of a linear position-sensitive detector 13. In each diffracted beam 8, electromagnetic radiation of different wavelengths propagates away from the surface of sensor element 1 under different angles. Spatial separation of diffracted beams 8 can be achieved by changing the period of diffraction grating 6 in each sensor area 12.

Example 3

FIG. 3 shows an embodiment of the method for multichannel SPR sensor detection using a sensor element 1 with multiple sensing areas 12 with a diffraction grating 6 which enables the coupling of an electromagnetic wave 3 to surface plasmons 2 and angular dispersing wavelength spectrum of the electromagnetic wave 3. Collimated electromagnetic wave 3 is made simultaneously incident on multiple sensing areas 12 which are arranged perpendicularly to the direction of propagation of surface plasmons. Through diffraction on gratings 6, at different sensing areas 12 the electromagnetic wave 3 is coupled to spatially separated divergent electromagnetic beams 8. The diffracted beams 8 propagate away from the surface of the sensor element 1 and are incident on different areas of a two-dimensional position-sensitive detector 14. In each diffracted beam 8, electromagnetic radiation of different wavelengths propagates away from the surface of sensor element 1 at a different angle.

Example 4

FIG. 4 shows an embodiment of the method for multichannel SPR sensor detection using a sensor element 1 with multiple sensing areas 12 with a diffraction grating 6 which enables the coupling of an electromagnetic wave 3 to surface plasmons 2 and angular dispersion of wavelength spectrum of the electromagnetic wave 3. Collimated electromagnetic wave 3 is made simultaneously incident on multiple sensing areas 12. In different sensing areas 12, diffraction gratings are oriented different with respect to the center of a two-dimensional position-sensitive detector. Through diffraction on diffraction gratings 6, at different sensing areas 12, the electromagnetic wave is coupled to spatially separated divergent electromagnetic beams 8. The diffracted beams 8 propagate away from the surface of the sensor element 1 and are incident on different areas of a two-dimensional position-sensitive detector 14. In each diffracted beam 8, electromagnetic radiation of different wavelengths propagates away from the surface of sensor element 1 at a different angle.

Example 5

FIG. 5 depicts an embodiment of a sensor element 1 for the method for the SPR sensor method described herein in the form of a planar slide 16 with an array of sensing areas 12. In each sensing area 12, there is a diffraction grating for the coupling of an electromagnetic wave 3 to surface plasmons 2 and for the angular dispersion of the wavelength spectrum of the electromagnetic wave 3.

INDUSTRIAL APPLICABILITY

The method according to the invention can be used in numerous areas such as a medical diagnostics (detection of biomedical markers), pharmaceutical industry (drug development), food industry (quality control, detection of harmful contaminants, foodborne pathogens and toxins), environmental protection (monitoring of pollution of water and atmosphere), warfare and security (detection of harmful compounds). 

1. A method for spectroscopy of surface plasmons, comprising: making an electromagnetic wave incident on a diffraction grating; simultaneously exciting surface plasmons on a medium coincident to the diffraction grating and causing dispersion of a wavelength spectrum of the electromagnetic wave through diffraction on the diffraction grating; and measuring changes in spatial distribution of intensity in the wavelength spectrum of the diffracted electromagnetic wave due to the excitation of the surface plasmons.
 2. The method according to claim 1, wherein the electromagnetic wave is simultaneously made incident on one or more of a plurality of such diffraction gratings and on different areas of the diffraction grating.
 3. The method according to claim 1, further comprising: emitting the electromagnetic wave from electromagnetic radiation sources comprising at least one or more of a plurality of monochromatic sources and at least one polychromatic source.
 4. The method according to claim 1, further comprising: measuring the spatial distribution of intensity of the diffracted electromagnetic wave with position sensitive detectors comprising one or more of a linear array of detectors and a two-dimensional array of detectors.
 5. The method according to claim 1, wherein the diffraction grating comprises at least one of a metal diffraction grating, a diffraction grating fully coated with a metal layer, and a diffraction grating partially coated with a metal layer.
 6. The method according to claim 1 further comprising: providing an area on a surface of the diffraction grating with a coating comprising at least one of a full layer of selected substances and a partial layer of selected substances.
 7. The method according to claim 4, wherein the position-sensitive detectors further comprise at least one of CCD, PDA, and CMOS detector modules.
 8. The method according to claim 5, wherein the fully coated metal layer and the partially coated metal layer each comprise one or more layers.
 9. The method according to claim 1, wherein the diffraction grating comprises a sensing element on a surface plasmon resonance sensor to detect chemical and biological substances.
 10. A system for spectroanalyzing surface plasmons, comprising: an electromagnetic radiation module to make an electromagnetic wave incident on a diffraction grating, wherein surface plasmons are excited on a medium coincident to the diffraction grating and dispersion of a wavelength spectrum of the electromagnetic wave through diffraction by the diffraction grating are simultaneously caused; and position-sensitive detectors to measure changes in spatial distribution of intensity in the wavelength spectrum of the diffracted electromagnetic wave due to the excitation of the surface plasmons.
 11. The system according to claim 10, wherein the electromagnetic wave is simultaneously made incident on one or more of a plurality of such diffraction gratings and on different areas of the diffraction grating.
 12. The system according to claim 10, wherein the electromagnetic radiation module comprises one or more of: a plurality of monochromatic sources; and at least one polychromatic source to emit the electromagnetic wave.
 13. The system according to claim 10, wherein the position-sensitive detectors comprise one or more of: a linear array of detectors and a two-dimensional array of detectors.
 14. The system according to claim 13, wherein the position-sensitive detectors further comprise at least one of CCD, PDA, and CMOS detector modules.
 15. The system according to claim 10, wherein the diffraction grating comprises at least one of a metal diffraction grating, a diffraction grating fully coated with a metal layer, and a diffraction grating partially coated with a metal layer.
 16. The system according to claim 15, wherein the fully coated metal layer and the partially coated metal layer each comprise one or more layers.
 17. The system according to claim 10, further comprising: an area on a surface of the diffraction grating with a coating comprising at least one of: a full layer of selected substances; and a partial layer of selected substances.
 18. The system according to claim 10, wherein the diffraction grating comprises a sensing element on a surface plasmon resonance sensor to detect chemical and biological substances.
 19. A method for constructing a surface plasmon resonance sensor, comprising: forming a sensor element with diffraction gratings arranged to simultaneously excite surface plasmons and disperse electromagnetic waves over a wavelength spectrum, providing an adjustment to the diffraction gratings to control spatial distribution of wavelength intensity of the dispersed electromagnetic waves; and orienting a position sensitive detector to measure changes in the spatial distribution of wavelength intensity caused by the excitation of the surface plasmons.
 20. The method according to claim 19, wherein the changes in the spatial distribution of wavelength intensity are measured with position sensitive detectors comprising one or more of a linear array of detectors and a two-dimensional array of detectors.
 21. The method according to claim 20, wherein the position-sensitive detectors further comprise at least one of CCD, PDA, and CMOS detector modules.
 22. The method according to claim 19, wherein the diffraction gratings comprise at least one of metal diffraction gratings, diffraction gratings fully coated with a metal layer, and diffraction gratings partially coated with a metal layer.
 23. The method according to claim 22, wherein the fully coated metal layer and the partially coated metal layer each comprise one or more layers.
 24. The method according to claim 19, further comprising: providing a sensing area on the sensor element with at least one of a full layer of selected substances and a partial layer of selected substances.
 25. The method according to claim 19, further comprising: adjusting the diffraction gratings based on at least one of geometry, orientation, and quantity.
 26. A system for constructing a surface plasmon resonance measurement sensor, comprising: a sensor element with diffraction gratings arranged to simultaneously excite surface plasmons and disperse electromagnetic waves over a wavelength spectrum, wherein the diffraction gratings are adjustable to control spatial distribution of wavelength intensity of the dispersed electromagnetic waves; and a position sensitive detector oriented to measure changes in the spatial distribution of wavelength intensity induced by the excitation of the surface plasmons.
 27. The system according to claim 26, further comprising: measuring the spatial distribution of intensity of the electromagnetic wave with position sensitive detectors comprising one or more of a linear array of detectors and a two-dimensional array of detectors.
 28. The system according to claim 27, wherein the position-sensitive detectors further comprise at least one of CCD, PDA, and CMOS detector modules.
 29. The system according to claim 26, wherein the diffraction grating comprises at least one of a metal diffraction grating, a diffraction grating fully coated with a metal layer, and a diffraction grating partially coated with a metal layer.
 30. The system according to claim 29, wherein the fully coated metal layer and the partially coated metal layer each comprise one or more layers.
 31. The system according to claim 26, further comprising: a sensing area on the sensor element with at least one of a full layer of selected substances and a partial layer of selected substances.
 32. The method according to claim 26, further comprising: adjusting the diffraction gratings based on at least one of geometry, orientation, and quantity. 